core: rm CommandContext.serialVersionUUID

Commit 3600344aa41e559ef6fa145c910e82421b194c13 changed CommandContext
to stop being Serializable, but neglected to remove the
serialVersionUUID. This patches rectifies that omission.

Change-Id: I1204da10d91c7a0435d65450b58f39f9dbf0c48f
Signed-off-by: Allon Mureinik <amureini@redhat.com>